This invention relates to improved multiple hem stitches for sewing up two superimposed materials and an apparatus for forming the multiple hem stitches used in combination with a sewing machine.
Typical types of overedge or hem stitches may be generally referred to as Stitch Types E12A and E13 specified by the Japanese Industrial Standard (JIS). The former type stitch E12A is formed with a sewing machine having one needle carrying a needle thread and one looper carrying a looper thread. The needle is vertically reciprocated to penetrate the fabric to form a thread loop beneath the underside of the fabric inwardly of the edge thereof. The loop is caused by the looper to extend to the fabric edge transversely thereof. The looper is further moved around the fabric edge to a position above the fabric into the moving path of the needle where the descending needle will catch the looper thread to interlock the needle thread and the looper thread to thereby form a hem stitch while the needle thread is tightened and the fabric is transported one step. The latter type stitch E13 is formed with a sewing machine having one needle carrying a needle thread and two loopers carrying first and second looper thread respectively. The needle is vertically reciprocated to penetrate the fabric to form a loop on the underside of the fabric. Then the first looper is operated to catch the loop of the needle thread. At the same time, the second looper is operated to catch the looper thread of the first looper. The second looper is further moved around the fabric edge into the moving path of the needle above the fabric, where the descending needle catches the second looper thread. Thus a specific hem stitch is formed with three threads properly interlocked to each other. However, both types of such conventional hem stitches may be satisfactory for simply hemming the fabric, but is not satisfactory for giving the effect of sewing up two or more of superimposed fabric beside hemming the same.
These hem stitches E12A and E13 can be more reinforced with an additional stitch for sewing up two or more fabrics besides simply hemming the same. Such an additional stitch may be the Stitch Type D12 of JIS comprising a needle thread and a looper thread interlocked with each other into a double-chain stitch. Such a reinforced type of the stitch (D12+E12A) may be formed by employing a pair of needles each carrying a needle thread and a pair of loopers each carrying a looper thread, or another reinforced type stitch (D12+E13) may be formed by employing a pair of needles and three loopers, and can be advantageously used for sewing up two or more superimposed fabrics hemming the edges thereof, and at the same time has sufficient stretch or elasticity in the seam. Moreover, the reinforced stitch will not be easily loosened even when a portion of the stitch is accidentally cut off. However, in a looper mechanism of a sewing machine adapted to form such reinforced stitches, there must be provided not only drive means for one or two loopers for forming the hem stitch portion E12A or E13 but also another independent driveC means for a looper for forming the double-chain stitch portion D12 which must be so designed as to prevent the looper from contacting the vertically reciprocating needle, resulting in a great probability of complicating the looper mechanism, and impeding the manufacturing cost reduction purpose. Thus, the hem stitch sewing machine manufactured with special intent to produce such reinforced stitches has, in practice, a limited application of use, that is usable for industrial purposes but is not suitable for domestic use irrespective of recently increasing demand therefor.